1. Field of the Invention
The present invention relates to a preparation process of a chemically amplified positive resist material used for micropatterning and sensitive to high energy radiation such as ultraviolet ray, far ultraviolet ray, electron beam, X ray, excimer laser, γ ray and synchrotron radiation.
2. Description of the Related Art
In the drive for higher integration of integrated circuits, formation of finer patterns is requested recently. As resists used for photolithography with KrF excimer laser light having a wavelength of 248 nm or exposure light having a shorter wavelength than it, or lithography with high energy radiation such as electron beam or X-ray, a chemically amplified resist is predominant because of its excellent sensitivity and resolution.
Chemically amplified resists include negative resists and positive resists. The negative resists (described, for example, in Japanese Patent Provisional Publication No. 2006-201532) essentially contain a binder soluble in an aqueous alkali solution, a crosslinking agent (in some cases, an agent serving both as a crosslinking agent and a binder) for crosslinking binders and insolubilizing them in the presence of an acid, and an acid generator which generates an acid when exposed to high energy radiation. The positive resists (described, for example, in Japanese Patent Provisional Publication No. 2006-225476 and Japanese Patent Provisional Publication No. 2006-124314), on the other hand, essentially contain a binder which is insoluble in an aqueous alkali solution but becomes alkali soluble after elimination of a protecting group in the presence of an acid and an acid generator.
When exposed to high energy radiation, a resist film containing the above-described materials undergoes a change in its solubility due to a catalytic reaction caused by an acid generated from the acid generator. It is extremely important for microfabrication to control a range within which the acid causes a catalytic reaction, that is, to control a diffusion distance of the acid, because small diffusion distance of the acid fails to achieve expected sensitivity, while large diffusion distance reduces a light/dark contrast and deteriorates the resolution performance. A basic compound serving to control this diffusion distance of the acid is therefore a substantially essential constituent material for either the positive resist or negative resist. Such a basic compound to be added to the resist composition is typically a nitrogenous basic substance. Many nitrogenous basic substances are known and disclosed, for example, in Japanese Patent Provisional Publication Nos. 2006-201532, 2006-225476 and 2006-124314.
In processing of a substrate with a chemically amplified resist, a resist film is formed by applying a solution of the above-described materials so that the resist composition further contains a solvent as an essential material.